The objectives of this project are to a)study some of the factors which influence extrarenal Ep production b) to develop a rat model for the anemia of uremia in which to study the effects of various androgenic and anabolic steroids and c) to investigate the mechanism of the amemia of protein depletion. a) Bilaterally nephrectomized rats will be infused continuously with various amounts of renin and of angiotensin while in an atmosphere containing 92 percent N2 and 8 percent O2. The plasma erythropoietin (Ep) level will be measured at 8 hours. b) Five-sixths of the renal mass of rats will be removed in a two part procedure. Theses rats become anemic and have BUN's over 100 gm/l00 ml. We will then determine the effects of injecting these rats with various amounts of testosterone or nortestosterone; or of feeding them methyltestosterone, fluoxymesterone, or oxymethalone, c) Rats will be put on protein free diets for periods of 1 to 14 days and its effect on their ability to produce Ep in response to 8 hours at 0.4 atmosphere will be measured. We will then determine the effect of feeding various amounts of protein or amino acids on EP production. Also we will measure the effect of implanting tumors, increasing erythropoiesis, or stimulating ferritin synthesis on the ability of protein depleted rats to make Ep in response to hypoxia and protein feeding.